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 $59.82   8.868%   $65.1248   $65.12   $65.10   $65.10  
  Purchase #2 $109.51   7.566%   $117.7955   $117.80   $117.80   $117.80  
  Purchase #3 $126.33   10.701%   $139.8486   $139.85   $139.85   $139.80  
  Purchase #4 $120.44   11.580%   $134.387   $134.39   $134.40   $134.40  
  Purchase #5 $87.40   9.846%   $96.0054   $96.01   $96.00   $96.00  
  Purchase #6 $187.40   7.471%   $201.4007   $201.40   $201.40   $201.40  
  Purchase #7 $247.90   7.538%   $266.5867   $266.59   $266.60   $266.60  
  7 purchase totals = $938.80       $1,021.1487   $1,021.16   $1,021.15   $1,021.10