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 $54.95   7.287%   $58.9542   $58.95   $58.95   $59.00  
  Purchase #2 $60.28   6.466%   $64.1777   $64.18   $64.20   $64.20  
  Purchase #3 $217.55   13.564%   $247.0585   $247.06   $247.05   $247.10  
  Purchase #4 $246.57   11.728%   $275.4877   $275.49   $275.50   $275.50  
  Purchase #5 $189.98   8.470%   $206.0713   $206.07   $206.05   $206.10  
  Purchase #6 $249.94   3.520%   $258.7379   $258.74   $258.75   $258.70  
  Purchase #7 $109.52   9.868%   $120.3274   $120.33   $120.35   $120.30  
  7 purchase totals = $1,128.79       $1,230.8147   $1,230.82   $1,230.85   $1,230.90