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 $69.39   6.284%   $73.7505   $73.75   $73.75   $73.80  
  Purchase #2 $136.84   13.298%   $155.037   $155.04   $155.05   $155.00  
  Purchase #3 $219.78   11.402%   $244.8393   $244.84   $244.85   $244.80  
  Purchase #4 $64.32   6.196%   $68.3053   $68.31   $68.30   $68.30  
  Purchase #5 $98.81   7.651%   $106.37   $106.37   $106.35   $106.40  
  Purchase #6 $205.64   13.556%   $233.5166   $233.52   $233.50   $233.50  
  Purchase #7 $150.68   7.147%   $161.4491   $161.45   $161.45   $161.40  
  7 purchase totals = $945.46       $1,043.2678   $1,043.28   $1,043.25   $1,043.20