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 $212.25   12.370%   $238.5053   $238.51   $238.50   $238.50  
  Purchase #2 $194.65   4.255%   $202.9324   $202.93   $202.95   $202.90  
  Purchase #3 $102.31   13.396%   $116.0154   $116.02   $116.00   $116.00  
  Purchase #4 $159.62   5.471%   $168.3528   $168.35   $168.35   $168.40  
  Purchase #5 $246.55   8.453%   $267.3909   $267.39   $267.40   $267.40  
  Purchase #6 $100.29   13.626%   $113.9555   $113.96   $113.95   $114.00  
  Purchase #7 $84.46   4.216%   $88.0208   $88.02   $88.00   $88.00  
  7 purchase totals = $1,100.13       $1,195.1731   $1,195.18   $1,195.15   $1,195.20