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 $71.35   10.179%   $78.6127   $78.61   $78.60   $78.60  
  Purchase #2 $58.66   9.159%   $64.0327   $64.03   $64.05   $64.00  
  Purchase #3 $165.74   9.683%   $181.7886   $181.79   $181.80   $181.80  
  Purchase #4 $132.60   4.261%   $138.2501   $138.25   $138.25   $138.30  
  Purchase #5 $198.50   9.803%   $217.959   $217.96   $217.95   $218.00  
  Purchase #6 $240.25   13.470%   $272.6117   $272.61   $272.60   $272.60  
  Purchase #7 $11.77   13.240%   $13.3283   $13.33   $13.35   $13.30  
  7 purchase totals = $878.87       $966.5831   $966.58   $966.60   $966.60