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 $58.89   10.399%   $65.014   $65.01   $65.00   $65.00  
  Purchase #2 $102.53   7.558%   $110.2792   $110.28   $110.30   $110.30  
  Purchase #3 $224.91   13.665%   $255.644   $255.64   $255.65   $255.60  
  Purchase #4 $219.91   6.789%   $234.8397   $234.84   $234.85   $234.80  
  Purchase #5 $96.59   6.122%   $102.5032   $102.50   $102.50   $102.50  
  Purchase #6 $113.59   11.666%   $126.8414   $126.84   $126.85   $126.80  
  Purchase #7 $60.35   5.219%   $63.4997   $63.50   $63.50   $63.50  
  7 purchase totals = $876.77       $958.6212   $958.61   $958.65   $958.50