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 $246.75   11.481%   $275.0794   $275.08   $275.10   $275.10  
  Purchase #2 $116.31   3.799%   $120.7286   $120.73   $120.75   $120.70  
  Purchase #3 $227.36   8.789%   $247.3427   $247.34   $247.35   $247.30  
  Purchase #4 $149.34   9.588%   $163.6587   $163.66   $163.65   $163.70  
  Purchase #5 $145.79   3.108%   $150.3212   $150.32   $150.30   $150.30  
  Purchase #6 $73.99   4.524%   $77.3373   $77.34   $77.35   $77.30  
  Purchase #7 $116.60   9.371%   $127.5266   $127.53   $127.55   $127.50  
  7 purchase totals = $1,076.14       $1,161.9945   $1,162.00   $1,162.05   $1,161.90