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 $70.92   3.407%   $73.3362   $73.34   $73.35   $73.30  
  Purchase #2 $59.33   13.132%   $67.1212   $67.12   $67.10   $67.10  
  Purchase #3 $147.36   3.611%   $152.6812   $152.68   $152.70   $152.70  
  Purchase #4 $243.57   11.588%   $271.7949   $271.79   $271.80   $271.80  
  Purchase #5 $211.78   3.124%   $218.396   $218.40   $218.40   $218.40  
  Purchase #6 $54.75   11.120%   $60.8382   $60.84   $60.85   $60.80  
  Purchase #7 $240.27   12.683%   $270.7434   $270.74   $270.75   $270.70  
  7 purchase totals = $1,027.98       $1,114.9111   $1,114.91   $1,114.95   $1,114.80