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 $196.98   13.219%   $223.0188   $223.02   $223.00   $223.00  
  Purchase #2 $184.43   13.364%   $209.0772   $209.08   $209.10   $209.10  
  Purchase #3 $152.59   9.306%   $166.79   $166.79   $166.80   $166.80  
  Purchase #4 $42.95   10.324%   $47.3842   $47.38   $47.40   $47.40  
  Purchase #5 $90.54   7.557%   $97.3821   $97.38   $97.40   $97.40  
  Purchase #6 $209.34   7.559%   $225.164   $225.16   $225.15   $225.20  
  Purchase #7 $83.52   6.299%   $88.7809   $88.78   $88.80   $88.80  
  7 purchase totals = $960.35       $1,057.5972   $1,057.59   $1,057.65   $1,057.70