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 $198.34   7.265%   $212.7494   $212.75   $212.75   $212.70  
  Purchase #2 $228.66   12.757%   $257.8302   $257.83   $257.85   $257.80  
  Purchase #3 $65.89   3.801%   $68.3945   $68.39   $68.40   $68.40  
  Purchase #4 $249.48   6.528%   $265.7661   $265.77   $265.75   $265.80  
  Purchase #5 $223.49   12.155%   $250.6552   $250.66   $250.65   $250.70  
  Purchase #6 $224.91   7.191%   $241.0833   $241.08   $241.10   $241.10  
  Purchase #7 $225.31   11.570%   $251.3784   $251.38   $251.40   $251.40  
  7 purchase totals = $1,416.08       $1,547.8571   $1,547.86   $1,547.90   $1,547.90