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 $38.54   6.743%   $41.1388   $41.14   $41.15   $41.10  
  Purchase #2 $132.47   11.679%   $147.9412   $147.94   $147.95   $147.90  
  Purchase #3 $61.56   12.407%   $69.1977   $69.20   $69.20   $69.20  
  Purchase #4 $74.74   11.226%   $83.1303   $83.13   $83.15   $83.10  
  Purchase #5 $130.47   6.806%   $139.3498   $139.35   $139.35   $139.30  
  Purchase #6 $196.26   4.322%   $204.7424   $204.74   $204.75   $204.70  
  Purchase #7 $68.57   9.755%   $75.259   $75.26   $75.25   $75.30  
  7 purchase totals = $702.61       $760.7592   $760.76   $760.80   $760.60