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 $87.31   11.496%   $97.3472   $97.35   $97.35   $97.30  
  Purchase #2 $221.58   5.434%   $233.6207   $233.62   $233.60   $233.60  
  Purchase #3 $120.85   3.839%   $125.4894   $125.49   $125.50   $125.50  
  Purchase #4 $165.42   3.205%   $170.7217   $170.72   $170.70   $170.70  
  Purchase #5 $247.57   12.342%   $278.1251   $278.13   $278.15   $278.10  
  Purchase #6 $127.83   3.238%   $131.9691   $131.97   $131.95   $132.00  
  Purchase #7 $211.50   10.133%   $232.9313   $232.93   $232.95   $232.90  
  7 purchase totals = $1,182.06       $1,270.2045   $1,270.21   $1,270.20   $1,270.10