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 $180.56   11.853%   $201.9618   $201.96   $201.95   $202.00  
  Purchase #2 $32.45   7.132%   $34.7643   $34.76   $34.75   $34.80  
  Purchase #3 $211.71   5.355%   $223.0471   $223.05   $223.05   $223.00  
  Purchase #4 $209.53   5.165%   $220.3522   $220.35   $220.35   $220.40  
  Purchase #5 $23.71   5.264%   $24.9581   $24.96   $24.95   $25.00  
  Purchase #6 $168.61   12.657%   $189.951   $189.95   $189.95   $190.00  
  Purchase #7 $209.32   8.614%   $227.3508   $227.35   $227.35   $227.40  
  7 purchase totals = $1,035.89       $1,122.3853   $1,122.38   $1,122.35   $1,122.60