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 $217.54   13.111%   $246.0617   $246.06   $246.05   $246.10  
  Purchase #2 $100.43   11.872%   $112.353   $112.35   $112.35   $112.40  
  Purchase #3 $121.31   4.751%   $127.0734   $127.07   $127.05   $127.10  
  Purchase #4 $187.62   8.107%   $202.8304   $202.83   $202.85   $202.80  
  Purchase #5 $167.58   5.674%   $177.0885   $177.09   $177.10   $177.10  
  Purchase #6 $121.42   11.740%   $135.6747   $135.67   $135.65   $135.70  
  Purchase #7 $64.82   9.855%   $71.208   $71.21   $71.20   $71.20  
  7 purchase totals = $980.72       $1,072.2897   $1,072.28   $1,072.25   $1,072.40