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 $53.52   8.453%   $58.044   $58.04   $58.05   $58.00  
  Purchase #2 $80.99   13.180%   $91.6645   $91.66   $91.65   $91.70  
  Purchase #3 $239.27   8.453%   $259.4955   $259.50   $259.50   $259.50  
  Purchase #4 $162.84   7.746%   $175.4536   $175.45   $175.45   $175.50  
  Purchase #5 $145.99   11.718%   $163.0971   $163.10   $163.10   $163.10  
  Purchase #6 $17.31   9.402%   $18.9375   $18.94   $18.95   $18.90  
  Purchase #7 $138.90   6.539%   $147.9827   $147.98   $148.00   $148.00  
  7 purchase totals = $838.82       $914.6749   $914.67   $914.70   $914.70