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 $95.31   12.357%   $107.0875   $107.09   $107.10   $107.10  
  Purchase #2 $203.76   10.639%   $225.438   $225.44   $225.45   $225.40  
  Purchase #3 $41.88   13.765%   $47.6448   $47.64   $47.65   $47.60  
  Purchase #4 $193.52   7.152%   $207.3606   $207.36   $207.35   $207.40  
  Purchase #5 $95.75   9.431%   $104.7802   $104.78   $104.80   $104.80  
  Purchase #6 $196.60   3.467%   $203.4161   $203.42   $203.40   $203.40  
  Purchase #7 $162.52   12.683%   $183.1324   $183.13   $183.15   $183.10  
  7 purchase totals = $989.34       $1,078.8596   $1,078.86   $1,078.90   $1,078.80