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 $240.46   10.588%   $265.9199   $265.92   $265.90   $265.90  
  Purchase #2 $215.55   7.319%   $231.3261   $231.33   $231.35   $231.30  
  Purchase #3 $10.73   4.180%   $11.1785   $11.18   $11.20   $11.20  
  Purchase #4 $129.97   13.630%   $147.6849   $147.68   $147.70   $147.70  
  Purchase #5 $200.79   13.654%   $228.2059   $228.21   $228.20   $228.20  
  Purchase #6 $54.82   9.462%   $60.0071   $60.01   $60.00   $60.00  
  Purchase #7 $8.66   12.157%   $9.7128   $9.71   $9.70   $9.70  
  7 purchase totals = $860.98       $954.0352   $954.04   $954.05   $954.00