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 $92.66   7.576%   $99.6799   $99.68   $99.70   $99.70  
  Purchase #2 $143.54   13.228%   $162.5275   $162.53   $162.55   $162.50  
  Purchase #3 $15.74   4.547%   $16.4557   $16.46   $16.45   $16.50  
  Purchase #4 $192.37   5.268%   $202.5041   $202.50   $202.50   $202.50  
  Purchase #5 $69.52   7.861%   $74.985   $74.99   $75.00   $75.00  
  Purchase #6 $213.45   11.502%   $238.001   $238.00   $238.00   $238.00  
  Purchase #7 $203.87   7.342%   $218.8381   $218.84   $218.85   $218.80  
  7 purchase totals = $931.15       $1,012.9913   $1,013.00   $1,013.05   $1,013.00