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 $91.49   4.385%   $95.5018   $95.50   $95.50   $95.50  
  Purchase #2 $80.67   11.137%   $89.6542   $89.65   $89.65   $89.70  
  Purchase #3 $213.94   11.117%   $237.7237   $237.72   $237.70   $237.70  
  Purchase #4 $59.81   5.325%   $62.9949   $62.99   $63.00   $63.00  
  Purchase #5 $133.72   11.836%   $149.5471   $149.55   $149.55   $149.50  
  Purchase #6 $202.33   9.108%   $220.7582   $220.76   $220.75   $220.80  
  Purchase #7 $186.58   12.460%   $209.8279   $209.83   $209.85   $209.80  
  7 purchase totals = $968.54       $1,066.0078   $1,066.00   $1,066.00   $1,066.00