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 $244.82   8.107%   $264.6676   $264.67   $264.65   $264.70  
  Purchase #2 $80.36   7.230%   $86.17   $86.17   $86.15   $86.20  
  Purchase #3 $238.28   13.242%   $269.833   $269.83   $269.85   $269.80  
  Purchase #4 $24.57   5.505%   $25.9226   $25.92   $25.90   $25.90  
  Purchase #5 $174.58   7.243%   $187.2248   $187.22   $187.20   $187.20  
  Purchase #6 $110.94   9.113%   $121.05   $121.05   $121.05   $121.10  
  Purchase #7 $20.84   3.460%   $21.5611   $21.56   $21.55   $21.60  
  7 purchase totals = $894.39       $976.4291   $976.42   $976.35   $976.50