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 $228.81   7.569%   $246.1286   $246.13   $246.15   $246.10  
  Purchase #2 $205.55   11.503%   $229.1944   $229.19   $229.20   $229.20  
  Purchase #3 $69.77   11.744%   $77.9638   $77.96   $77.95   $78.00  
  Purchase #4 $201.53   10.661%   $223.0151   $223.02   $223.00   $223.00  
  Purchase #5 $72.28   10.127%   $79.5998   $79.60   $79.60   $79.60  
  Purchase #6 $110.98   8.647%   $120.5764   $120.58   $120.60   $120.60  
  Purchase #7 $43.44   12.685%   $48.9504   $48.95   $48.95   $49.00  
  7 purchase totals = $932.36       $1,025.4285   $1,025.43   $1,025.45   $1,025.50