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 $237.89   11.746%   $265.8326   $265.83   $265.85   $265.80  
  Purchase #2 $101.75   8.415%   $110.3123   $110.31   $110.30   $110.30  
  Purchase #3 $228.67   6.676%   $243.936   $243.94   $243.95   $243.90  
  Purchase #4 $37.28   9.494%   $40.8194   $40.82   $40.80   $40.80  
  Purchase #5 $104.94   5.665%   $110.8849   $110.88   $110.90   $110.90  
  Purchase #6 $168.53   9.175%   $183.9926   $183.99   $184.00   $184.00  
  Purchase #7 $132.52   9.412%   $144.9928   $144.99   $145.00   $145.00  
  7 purchase totals = $1,011.58       $1,100.7706   $1,100.76   $1,100.80   $1,100.70