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 $148.95   8.115%   $161.0373   $161.04   $161.05   $161.00  
  Purchase #2 $242.56   10.463%   $267.9391   $267.94   $267.95   $267.90  
  Purchase #3 $209.79   7.195%   $224.8844   $224.88   $224.90   $224.90  
  Purchase #4 $106.36   7.219%   $114.0381   $114.04   $114.05   $114.00  
  Purchase #5 $163.29   7.651%   $175.7833   $175.78   $175.80   $175.80  
  Purchase #6 $92.26   11.485%   $102.8561   $102.86   $102.85   $102.90  
  Purchase #7 $19.94   10.719%   $22.0774   $22.08   $22.10   $22.10  
  7 purchase totals = $983.15       $1,068.6157   $1,068.62   $1,068.70   $1,068.60