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 $207.56   9.204%   $226.6638   $226.66   $226.65   $226.70  
  Purchase #2 $151.51   7.705%   $163.1838   $163.18   $163.20   $163.20  
  Purchase #3 $23.58   4.499%   $24.6409   $24.64   $24.65   $24.60  
  Purchase #4 $172.28   6.336%   $183.1957   $183.20   $183.20   $183.20  
  Purchase #5 $137.71   10.437%   $152.0828   $152.08   $152.10   $152.10  
  Purchase #6 $43.47   3.485%   $44.9849   $44.98   $45.00   $45.00  
  Purchase #7 $166.91   12.765%   $188.2161   $188.22   $188.20   $188.20  
  7 purchase totals = $903.02       $982.9680   $982.96   $983.00   $983.00