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 $136.52   9.292%   $149.2054   $149.21   $149.20   $149.20  
  Purchase #2 $120.56   3.456%   $124.7266   $124.73   $124.75   $124.70  
  Purchase #3 $54.75   5.210%   $57.6025   $57.60   $57.60   $57.60  
  Purchase #4 $171.95   3.868%   $178.601   $178.60   $178.60   $178.60  
  Purchase #5 $55.97   9.221%   $61.131   $61.13   $61.15   $61.10  
  Purchase #6 $237.74   3.786%   $246.7408   $246.74   $246.75   $246.70  
  Purchase #7 $239.85   11.302%   $266.9578   $266.96   $266.95   $267.00  
  7 purchase totals = $1,017.34       $1,084.9651   $1,084.97   $1,085.00   $1,084.90