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 $173.26   12.297%   $194.5658   $194.57   $194.55   $194.60  
  Purchase #2 $208.50   10.654%   $230.7136   $230.71   $230.70   $230.70  
  Purchase #3 $68.73   3.577%   $71.1885   $71.19   $71.20   $71.20  
  Purchase #4 $173.59   9.217%   $189.5898   $189.59   $189.60   $189.60  
  Purchase #5 $165.79   4.285%   $172.8941   $172.89   $172.90   $172.90  
  Purchase #6 $138.98   5.773%   $147.0033   $147.00   $147.00   $147.00  
  Purchase #7 $203.49   13.132%   $230.2123   $230.21   $230.20   $230.20  
  7 purchase totals = $1,132.34       $1,236.1674   $1,236.16   $1,236.15   $1,236.20