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 $143.45   11.507%   $159.9568   $159.96   $159.95   $160.00  
  Purchase #2 $42.25   13.795%   $48.0784   $48.08   $48.10   $48.10  
  Purchase #3 $109.57   5.636%   $115.7454   $115.75   $115.75   $115.70  
  Purchase #4 $50.56   9.326%   $55.2752   $55.28   $55.30   $55.30  
  Purchase #5 $39.32   6.814%   $41.9993   $42.00   $42.00   $42.00  
  Purchase #6 $29.56   5.705%   $31.2464   $31.25   $31.25   $31.20  
  Purchase #7 $231.63   4.270%   $241.5206   $241.52   $241.50   $241.50  
  7 purchase totals = $646.34       $693.8221   $693.84   $693.85   $693.80