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 $245.50   7.656%   $264.2955   $264.30   $264.30   $264.30  
  Purchase #2 $59.46   10.557%   $65.7372   $65.74   $65.75   $65.70  
  Purchase #3 $11.87   10.635%   $13.1324   $13.13   $13.15   $13.10  
  Purchase #4 $223.99   13.526%   $254.2869   $254.29   $254.30   $254.30  
  Purchase #5 $23.70   6.674%   $25.2817   $25.28   $25.30   $25.30  
  Purchase #6 $241.92   13.644%   $274.9276   $274.93   $274.95   $274.90  
  Purchase #7 $165.29   10.422%   $182.5165   $182.52   $182.50   $182.50  
  7 purchase totals = $971.73       $1,080.1778   $1,080.19   $1,080.25   $1,080.10