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 $116.95   9.753%   $128.3561   $128.36   $128.35   $128.40  
  Purchase #2 $59.47   4.297%   $62.0254   $62.03   $62.05   $62.00  
  Purchase #3 $105.49   4.294%   $110.0197   $110.02   $110.00   $110.00  
  Purchase #4 $58.66   7.148%   $62.853   $62.85   $62.85   $62.90  
  Purchase #5 $41.70   7.107%   $44.6636   $44.66   $44.65   $44.70  
  Purchase #6 $165.40   5.645%   $174.7368   $174.74   $174.75   $174.70  
  Purchase #7 $126.94   12.851%   $143.2531   $143.25   $143.25   $143.30  
  7 purchase totals = $674.61       $725.9077   $725.91   $725.90   $726.00