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 $95.38   8.107%   $103.1125   $103.11   $103.10   $103.10  
  Purchase #2 $202.70   3.118%   $209.0202   $209.02   $209.00   $209.00  
  Purchase #3 $248.96   3.360%   $257.3251   $257.33   $257.35   $257.30  
  Purchase #4 $45.26   8.644%   $49.1723   $49.17   $49.15   $49.20  
  Purchase #5 $176.66   9.761%   $193.9038   $193.90   $193.90   $193.90  
  Purchase #6 $203.51   3.549%   $210.7326   $210.73   $210.75   $210.70  
  Purchase #7 $165.74   9.814%   $182.0057   $182.01   $182.00   $182.00  
  7 purchase totals = $1,138.21       $1,205.2722   $1,205.27   $1,205.25   $1,205.20