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 $203.80   7.754%   $219.6027   $219.60   $219.60   $219.60  
  Purchase #2 $211.84   11.437%   $236.0681   $236.07   $236.05   $236.10  
  Purchase #3 $245.84   9.244%   $268.5654   $268.57   $268.55   $268.60  
  Purchase #4 $51.34   8.814%   $55.8651   $55.87   $55.85   $55.90  
  Purchase #5 $250.36   13.199%   $283.405   $283.41   $283.40   $283.40  
  Purchase #6 $241.50   6.400%   $256.956   $256.96   $256.95   $257.00  
  Purchase #7 $19.52   13.808%   $22.2153   $22.22   $22.20   $22.20  
  7 purchase totals = $1,224.20       $1,342.6776   $1,342.70   $1,342.60   $1,342.80