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 $211.66   10.624%   $234.1468   $234.15   $234.15   $234.10  
  Purchase #2 $110.74   9.231%   $120.9624   $120.96   $120.95   $121.00  
  Purchase #3 $150.80   4.272%   $157.2422   $157.24   $157.25   $157.20  
  Purchase #4 $138.31   9.437%   $151.3623   $151.36   $151.35   $151.40  
  Purchase #5 $66.33   13.386%   $75.2089   $75.21   $75.20   $75.20  
  Purchase #6 $143.65   5.565%   $151.6441   $151.64   $151.65   $151.60  
  Purchase #7 $154.62   10.343%   $170.6123   $170.61   $170.60   $170.60  
  7 purchase totals = $976.11       $1,061.1790   $1,061.17   $1,061.15   $1,061.10