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 $126.31   10.787%   $139.9351   $139.94   $139.95   $139.90  
  Purchase #2 $205.93   13.740%   $234.2248   $234.22   $234.20   $234.20  
  Purchase #3 $89.26   6.173%   $94.77   $94.77   $94.75   $94.80  
  Purchase #4 $84.97   10.507%   $93.8978   $93.90   $93.90   $93.90  
  Purchase #5 $138.80   12.806%   $156.5747   $156.57   $156.55   $156.60  
  Purchase #6 $242.37   6.447%   $257.9956   $258.00   $258.00   $258.00  
  Purchase #7 $65.65   7.755%   $70.7412   $70.74   $70.75   $70.70  
  7 purchase totals = $953.29       $1,048.1392   $1,048.14   $1,048.10   $1,048.10