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 $148.91   12.142%   $166.9907   $166.99   $167.00   $167.00  
  Purchase #2 $183.70   11.706%   $205.2039   $205.20   $205.20   $205.20  
  Purchase #3 $9.96   10.745%   $11.0302   $11.03   $11.05   $11.00  
  Purchase #4 $84.93   6.831%   $90.7316   $90.73   $90.75   $90.70  
  Purchase #5 $95.43   13.835%   $108.6327   $108.63   $108.65   $108.60  
  Purchase #6 $219.28   8.349%   $237.5877   $237.59   $237.60   $237.60  
  Purchase #7 $64.46   6.322%   $68.5352   $68.54   $68.55   $68.50  
  7 purchase totals = $806.67       $888.7120   $888.71   $888.80   $888.60