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 $60.30   10.579%   $66.6791   $66.68   $66.70   $66.70  
  Purchase #2 $211.90   6.657%   $226.0062   $226.01   $226.00   $226.00  
  Purchase #3 $204.41   8.858%   $222.5166   $222.52   $222.50   $222.50  
  Purchase #4 $123.58   11.529%   $137.8275   $137.83   $137.85   $137.80  
  Purchase #5 $118.41   12.631%   $133.3664   $133.37   $133.35   $133.40  
  Purchase #6 $96.44   8.344%   $104.487   $104.49   $104.50   $104.50  
  Purchase #7 $129.85   8.396%   $140.7522   $140.75   $140.75   $140.80  
  7 purchase totals = $944.89       $1,031.6350   $1,031.65   $1,031.65   $1,031.70