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 $208.94   12.518%   $235.0951   $235.10   $235.10   $235.10  
  Purchase #2 $67.49   5.196%   $70.9968   $71.00   $71.00   $71.00  
  Purchase #3 $156.44   11.308%   $174.1302   $174.13   $174.15   $174.10  
  Purchase #4 $78.58   12.448%   $88.3616   $88.36   $88.35   $88.40  
  Purchase #5 $142.61   4.316%   $148.765   $148.77   $148.75   $148.80  
  Purchase #6 $95.68   4.816%   $100.2879   $100.29   $100.30   $100.30  
  Purchase #7 $238.29   13.502%   $270.4639   $270.46   $270.45   $270.50  
  7 purchase totals = $988.03       $1,088.1005   $1,088.11   $1,088.10   $1,088.20