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 $123.94   4.793%   $129.8804   $129.88   $129.90   $129.90  
  Purchase #2 $225.54   3.102%   $232.5363   $232.54   $232.55   $232.50  
  Purchase #3 $55.58   3.446%   $57.4953   $57.50   $57.50   $57.50  
  Purchase #4 $205.89   3.433%   $212.9582   $212.96   $212.95   $213.00  
  Purchase #5 $48.68   5.469%   $51.3423   $51.34   $51.35   $51.30  
  Purchase #6 $205.97   11.121%   $228.8759   $228.88   $228.90   $228.90  
  Purchase #7 $105.49   12.832%   $119.0265   $119.03   $119.05   $119.00  
  7 purchase totals = $971.09       $1,032.1149   $1,032.13   $1,032.20   $1,032.10