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 $218.99   12.434%   $246.2192   $246.22   $246.20   $246.20  
  Purchase #2 $53.53   12.442%   $60.1902   $60.19   $60.20   $60.20  
  Purchase #3 $172.98   10.449%   $191.0547   $191.05   $191.05   $191.10  
  Purchase #4 $194.82   3.757%   $202.1394   $202.14   $202.15   $202.10  
  Purchase #5 $131.83   11.819%   $147.411   $147.41   $147.40   $147.40  
  Purchase #6 $100.74   5.692%   $106.4741   $106.47   $106.45   $106.50  
  Purchase #7 $48.39   11.754%   $54.0778   $54.08   $54.10   $54.10  
  7 purchase totals = $921.28       $1,007.5664   $1,007.56   $1,007.55   $1,007.60