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 $188.33   11.498%   $209.9842   $209.98   $210.00   $210.00  
  Purchase #2 $141.28   8.295%   $152.9992   $153.00   $153.00   $153.00  
  Purchase #3 $36.56   13.561%   $41.5179   $41.52   $41.50   $41.50  
  Purchase #4 $221.59   4.488%   $231.535   $231.54   $231.55   $231.50  
  Purchase #5 $44.89   5.196%   $47.2225   $47.22   $47.20   $47.20  
  Purchase #6 $96.66   5.727%   $102.1957   $102.20   $102.20   $102.20  
  Purchase #7 $6.48   8.751%   $7.0471   $7.05   $7.05   $7.00  
  7 purchase totals = $735.79       $792.5016   $792.51   $792.50   $792.40