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 $112.43   9.345%   $122.9366   $122.94   $122.95   $122.90  
  Purchase #2 $244.49   5.327%   $257.514   $257.51   $257.50   $257.50  
  Purchase #3 $25.53   4.226%   $26.6089   $26.61   $26.60   $26.60  
  Purchase #4 $159.66   4.298%   $166.5222   $166.52   $166.50   $166.50  
  Purchase #5 $49.65   11.350%   $55.2853   $55.29   $55.30   $55.30  
  Purchase #6 $181.28   4.790%   $189.9633   $189.96   $189.95   $190.00  
  Purchase #7 $220.51   13.147%   $249.5004   $249.50   $249.50   $249.50  
  7 purchase totals = $993.55       $1,068.3307   $1,068.33   $1,068.30   $1,068.30