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 $80.41   5.763%   $85.044   $85.04   $85.05   $85.00  
  Purchase #2 $106.45   6.154%   $113.0009   $113.00   $113.00   $113.00  
  Purchase #3 $147.82   7.623%   $159.0883   $159.09   $159.10   $159.10  
  Purchase #4 $215.82   12.226%   $242.2062   $242.21   $242.20   $242.20  
  Purchase #5 $154.68   3.629%   $160.2933   $160.29   $160.30   $160.30  
  Purchase #6 $203.56   3.809%   $211.3136   $211.31   $211.30   $211.30  
  Purchase #7 $75.34   9.369%   $82.3986   $82.40   $82.40   $82.40  
  7 purchase totals = $984.08       $1,053.3449   $1,053.34   $1,053.35   $1,053.30