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 $216.44   13.435%   $245.5187   $245.52   $245.50   $245.50  
  Purchase #2 $211.65   8.803%   $230.2815   $230.28   $230.30   $230.30  
  Purchase #3 $243.58   13.269%   $275.9006   $275.90   $275.90   $275.90  
  Purchase #4 $26.83   3.778%   $27.8436   $27.84   $27.85   $27.80  
  Purchase #5 $117.27   11.495%   $130.7502   $130.75   $130.75   $130.80  
  Purchase #6 $178.62   5.494%   $188.4334   $188.43   $188.45   $188.40  
  Purchase #7 $31.72   12.654%   $35.7338   $35.73   $35.75   $35.70  
  7 purchase totals = $1,026.11       $1,134.4618   $1,134.45   $1,134.50   $1,134.40