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 $151.32   10.814%   $167.6837   $167.68   $167.70   $167.70  
  Purchase #2 $114.54   6.374%   $121.8408   $121.84   $121.85   $121.80  
  Purchase #3 $25.91   4.727%   $27.1348   $27.13   $27.15   $27.10  
  Purchase #4 $159.64   10.564%   $176.5044   $176.50   $176.50   $176.50  
  Purchase #5 $158.82   11.830%   $177.6084   $177.61   $177.60   $177.60  
  Purchase #6 $169.25   6.363%   $180.0194   $180.02   $180.00   $180.00  
  Purchase #7 $11.82   10.148%   $13.0195   $13.02   $13.00   $13.00  
  7 purchase totals = $791.30       $863.8110   $863.80   $863.80   $863.70