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 $227.48   8.282%   $246.3199   $246.32   $246.30   $246.30  
  Purchase #2 $36.52   7.698%   $39.3313   $39.33   $39.35   $39.30  
  Purchase #3 $115.27   4.564%   $120.5309   $120.53   $120.55   $120.50  
  Purchase #4 $222.76   8.346%   $241.3515   $241.35   $241.35   $241.40  
  Purchase #5 $180.37   5.324%   $189.9729   $189.97   $189.95   $190.00  
  Purchase #6 $126.39   7.219%   $135.5141   $135.51   $135.50   $135.50  
  Purchase #7 $144.93   10.402%   $160.0056   $160.01   $160.00   $160.00  
  7 purchase totals = $1,053.72       $1,133.0262   $1,133.02   $1,133.00   $1,133.00