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 $241.34   8.815%   $262.6141   $262.61   $262.60   $262.60  
  Purchase #2 $6.33   9.429%   $6.9269   $6.93   $6.95   $6.90  
  Purchase #3 $191.60   11.438%   $213.5152   $213.52   $213.50   $213.50  
  Purchase #4 $153.64   10.184%   $169.2867   $169.29   $169.30   $169.30  
  Purchase #5 $205.36   11.289%   $228.5431   $228.54   $228.55   $228.50  
  Purchase #6 $41.64   6.842%   $44.489   $44.49   $44.50   $44.50  
  Purchase #7 $93.35   9.357%   $102.0848   $102.08   $102.10   $102.10  
  7 purchase totals = $933.26       $1,027.4598   $1,027.46   $1,027.50   $1,027.40