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 $64.76   5.472%   $68.3037   $68.30   $68.30   $68.30  
  Purchase #2 $57.55   7.318%   $61.7615   $61.76   $61.75   $61.80  
  Purchase #3 $140.37   3.331%   $145.0457   $145.05   $145.05   $145.00  
  Purchase #4 $250.35   5.236%   $263.4583   $263.46   $263.45   $263.50  
  Purchase #5 $177.78   13.293%   $201.4123   $201.41   $201.40   $201.40  
  Purchase #6 $89.56   7.506%   $96.2824   $96.28   $96.30   $96.30  
  Purchase #7 $187.92   11.599%   $209.7168   $209.72   $209.70   $209.70  
  7 purchase totals = $968.29       $1,045.9807   $1,045.98   $1,045.95   $1,046.00