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 $52.93   12.701%   $59.6526   $59.65   $59.65   $59.70  
  Purchase #2 $232.77   9.270%   $254.3478   $254.35   $254.35   $254.30  
  Purchase #3 $34.97   12.242%   $39.251   $39.25   $39.25   $39.30  
  Purchase #4 $23.85   4.295%   $24.8744   $24.87   $24.85   $24.90  
  Purchase #5 $141.38   3.457%   $146.2675   $146.27   $146.25   $146.30  
  Purchase #6 $62.31   9.626%   $68.308   $68.31   $68.30   $68.30  
  Purchase #7 $243.50   13.775%   $277.0421   $277.04   $277.05   $277.00  
  7 purchase totals = $791.71       $869.7434   $869.74   $869.70   $869.80