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 $61.49   11.427%   $68.5165   $68.52   $68.50   $68.50  
  Purchase #2 $155.47   10.415%   $171.6622   $171.66   $171.65   $171.70  
  Purchase #3 $63.84   4.847%   $66.9343   $66.93   $66.95   $66.90  
  Purchase #4 $202.43   13.398%   $229.5516   $229.55   $229.55   $229.60  
  Purchase #5 $102.36   7.463%   $109.9991   $110.00   $110.00   $110.00  
  Purchase #6 $108.50   4.149%   $113.0017   $113.00   $113.00   $113.00  
  Purchase #7 $152.74   12.346%   $171.5973   $171.60   $171.60   $171.60  
  7 purchase totals = $846.83       $931.2627   $931.26   $931.25   $931.30