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 $140.40   7.755%   $151.288   $151.29   $151.30   $151.30  
  Purchase #2 $109.32   9.610%   $119.8257   $119.83   $119.85   $119.80  
  Purchase #3 $11.65   8.463%   $12.6359   $12.64   $12.65   $12.60  
  Purchase #4 $56.52   3.657%   $58.5869   $58.59   $58.60   $58.60  
  Purchase #5 $205.35   7.345%   $220.433   $220.43   $220.45   $220.40  
  Purchase #6 $19.35   6.229%   $20.5553   $20.56   $20.55   $20.60  
  Purchase #7 $154.26   3.265%   $159.2966   $159.30   $159.30   $159.30  
  7 purchase totals = $696.85       $742.6214   $742.64   $742.70   $742.60