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 $244.35   5.849%   $258.642   $258.64   $258.65   $258.60  
  Purchase #2 $198.84   10.497%   $219.7122   $219.71   $219.70   $219.70  
  Purchase #3 $50.47   10.595%   $55.8173   $55.82   $55.80   $55.80  
  Purchase #4 $58.30   5.665%   $61.6027   $61.60   $61.60   $61.60  
  Purchase #5 $160.74   4.471%   $167.9267   $167.93   $167.95   $167.90  
  Purchase #6 $30.68   7.596%   $33.0105   $33.01   $33.00   $33.00  
  Purchase #7 $225.45   9.785%   $247.5103   $247.51   $247.50   $247.50  
  7 purchase totals = $968.83       $1,044.2217   $1,044.22   $1,044.20   $1,044.10