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 $213.29   3.462%   $220.6741   $220.67   $220.65   $220.70  
  Purchase #2 $22.31   11.219%   $24.813   $24.81   $24.80   $24.80  
  Purchase #3 $196.49   4.700%   $205.725   $205.73   $205.75   $205.70  
  Purchase #4 $60.83   7.273%   $65.2542   $65.25   $65.25   $65.30  
  Purchase #5 $243.88   12.231%   $273.709   $273.71   $273.70   $273.70  
  Purchase #6 $145.52   7.140%   $155.9101   $155.91   $155.90   $155.90  
  Purchase #7 $87.46   11.267%   $97.3141   $97.31   $97.30   $97.30  
  7 purchase totals = $969.78       $1,043.3995   $1,043.39   $1,043.35   $1,043.40