Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $157.98   5.711%   $167.0022   $167.00   $167.00   $167.00  
  Purchase #2 $177.89   3.167%   $183.5238   $183.52   $183.50   $183.50  
  Purchase #3 $246.76   13.841%   $280.9141   $280.91   $280.90   $280.90  
  Purchase #4 $206.38   9.654%   $226.3039   $226.30   $226.30   $226.30  
  Purchase #5 $170.99   6.764%   $182.5558   $182.56   $182.55   $182.60  
  Purchase #6 $244.29   11.244%   $271.758   $271.76   $271.75   $271.80  
  Purchase #7 $182.35   9.296%   $199.3013   $199.30   $199.30   $199.30  
  7 purchase totals = $1,386.64       $1,511.3591   $1,511.35   $1,511.30   $1,511.40