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 $93.84   10.754%   $103.9316   $103.93   $103.95   $103.90  
  Purchase #2 $56.34   11.245%   $62.6754   $62.68   $62.70   $62.70  
  Purchase #3 $94.65   9.585%   $103.7222   $103.72   $103.70   $103.70  
  Purchase #4 $138.33   5.244%   $145.584   $145.58   $145.60   $145.60  
  Purchase #5 $206.56   7.723%   $222.5126   $222.51   $222.50   $222.50  
  Purchase #6 $221.66   4.674%   $232.0204   $232.02   $232.00   $232.00  
  Purchase #7 $178.92   11.739%   $199.9234   $199.92   $199.90   $199.90  
  7 purchase totals = $990.30       $1,070.3696   $1,070.36   $1,070.35   $1,070.30