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 $78.77   12.463%   $88.5871   $88.59   $88.60   $88.60  
  Purchase #2 $211.99   10.824%   $234.9358   $234.94   $234.95   $234.90  
  Purchase #3 $81.32   7.622%   $87.5182   $87.52   $87.50   $87.50  
  Purchase #4 $243.77   13.608%   $276.9422   $276.94   $276.95   $276.90  
  Purchase #5 $52.64   10.779%   $58.3141   $58.31   $58.30   $58.30  
  Purchase #6 $132.45   6.493%   $141.05   $141.05   $141.05   $141.10  
  Purchase #7 $177.42   13.337%   $201.0825   $201.08   $201.10   $201.10  
  7 purchase totals = $978.36       $1,088.4299   $1,088.43   $1,088.45   $1,088.40